1. Field of the Invention
This invention relates to a recording medium for recording information signals and a disc cartridge holding the recording medium therein.
2. Description of Related Art
Up to now, a recording medium for recording information signals on the major surface of a flexible disc substrate which is the signal recording surface, has been in use.
A magnetic disc employing a flexible disc substrate, with a diameter of 3.5 inch has been in use. This magnetic disc has a center hub for chucking the magnetic disc on a disc drive device. The magnetic disc, so far used extensively, has a recording capacity of 2 megabyte (MB).
A magnetic disc 200, currently in widespread use, has a flexible disc substrate 201 of synthetic resin, and has the major surface of the disc substrate as the signal recording surface, as shown in FIGS. 1 and 2. At the center of the disc substrate 201 is formed a circular center aperture 201a and a hub 202 is mounted for closing this center aperture 201a.
The hub 202 is formed of a magnetic material, such as iron, and is mounted on the disc substrate 201 by having its tubular protruding portion 202a fitted in the center aperture 201a and by having its flange portion 202d on the outer rim of the protruding portion secured by adhesion to the rim of the center aperture 201a. In the center of the hub 202 is formed a rectangular spindle passage opening 202b passed through by a spindle 221 provided on the disc drive device side. At an offset portion from the center portion is formed a rectangular chuck pin engagement opening 202c engaged by a chuck pin 223 provided on the disc drive device.
The distal end face of the protruding portion 202a of the hub 202, formed with the spindle passage opening 202b and the chuck pin engagement opening 202c, operates as a setting surface 202e on a disc supporting surface 222a of a disc table 222 provided on the driving device. The outer rim portion of the setting surface 202e operates as a suction portion by a magnet 224 provided on the outer rim of the disc supporting surface 222a.
The magnetic disc 200, constructed as described above, is rotated in unison with the disc table by having its hub 202 chucked and centered with respect to a disc table of a disc rotation unit 220 provided on the disc drive device side. The information signals are recorded and/or reproduced by actuating the magnetic disc 200 by the magnetic head.
The disc rotation unit 220, provided on the disc drive device side, loaded with the magnetic disc 200, has the disc table 222 mounted as-one on the distal end of the spindle 221 run in rotation by a spindle motor, not shown. The upper side of the disc table 222, carried at the distal end of the spindle 221, operates as the disc supporting surface 222a on which to set the hub 202 of the magnetic disc 200. A chuck pin 223 is mounted at a position on the disc table 222 offset from the spindle 221. The chuck pin 223 is mounted for movement in a direction emerging from and sinking into the disc supporting surface 222a and in a direction towards and away from the spindle 221. The chuck pin 223 is biased in a direction away from the spindle 221 by biasing means, not shown.
On the disc table 222 is mounted a magnet 224, formed as, for example, a annular rubber magnet, for surrounding the disc supporting surface 222a. The magnet 224 is mounted on the disc table 222 so as to be at a lower level than the disc supporting surface 222a of the magnetic disc 200 on which to set the hub 202. There is maintained a pre-set separation H.sub.0 between the magnet and the setting surface 202e of the hub 202 on the disc supporting surface 222a, as shown in FIG. 4.
The magnetic disc 200 is chucked on the disc table 222 by introducing the the spindle 221 through the spindle passage opening 202b, engaging the chuck pin 223 in the chuck pin engagement opening 202c, and by setting the setting surface 202e on the disc supporting surface 222a of the disc table 222, the hub 202 being then sucked by the hub 202, as shown in FIG. 4.
The state in which the magnetic disc 200 is mounted on the disc table 222 is explained.
In an initial state when the magnetic disc 200 is set on the disc table 222, the spindle 221 is passed through the spindle passage opening 202b and the chuck in 223 is engaged in the chuck pin engagement opening 202c, the spindle 221 and the chuck pin 223 usually are inserted into or engaged in the spindle passage opening 202b and in the chuck pin engagement opening 202c, without being thrust by the internal surfaces of these openings. At this time, the center-to-center separation F between the spindle 221 and the chuck pin 223 is the separation in an initial state in which the chuck pin 223 is not moved towards the outer rim of the magnetic disc 200.
The spindle passage opening 202b has the shape of a rectangle having a side of a length D and rounded at four corners. The spindle 221, introduced into the spindle passage opening 202b, has the shape of a column having diameter .phi.E shorter than the length D of a side of the spindle passage opening 202b. The chuck pin engagement opening 202c has the shape of a rectangle having the lengths of long and short sides equal to A and B, respectively, and having arcuately-shaped corners, as shown in FIG. 5. The chuck pin 223, engaged in the chuck pin engagement opening 202c, has the shape of a column having a diameter .phi.C shorter than the length B of the short side of the chuck pin engagement opening 202c.
If, from the state shown in FIG. 5 in which the magnetic disc 200 is set on the disc table 222, with the spindle 221 passed through the spindle passage opening 202b and the chuck pin 223 engaged in the chuck pin engagement opening 202c, the disc table 222 is run in rotation in the direction indicated by arrow R in FIG. 5, the chuck pin 223 compresses against the outer corner of the chuck pin engagement opening 202c towards the rotating direction of the disc table 222 to move the magnetic disc 200 towards the outer rim of the spindle 221, as shown in FIG. 6. By the magnetic disc 200 bing moved towards the rim by the chuck pin 223, the spindle 221 compresses against the corner of the spindle passage opening 202b remotest from the corner of the chuck pin engagement opening 202c engaged by the chuck pin 223, as shown in FIG. 6, thus centering the hub 202 of the magnetic disc 200 with respect to the disc table 222.
When the hub 202 of the magnetic disc 200 is centered on the disc table 22, there is produced difference between the rotational speed of the disc table 222 and that of the magnetic disc 200. That is, the disc table 222 is rotated n advance of the magnetic disc, such that the chuck pin 221 compresses against the outer corner of the chuck pin engagement opening 202c disposed towards the rotational direction of the disc table 222. By the chuck pin 221 compressing against the chuck pin engagement opening 202c, the magnetic disc 200 is moved from the center towards the outer rim of the spindle 221, under the bias of the chuck pin 221 biased in the direction of the outer rim of the disc table 222, the spindle 221 compressing against the corner of the spindle passage opening 202b for centering the hub 202 with respect to the disc table 222. At this time, the chuck pin 221 is moved towards the inner rim of the hub 202 to reduce the center-to-center distance G between the spindle 221 and the chuck pin 223 to a value smaller than the initial state distance F shown in FIG. 5.
The magnetic disc 200 is sucked by a magnet 224 on the disc table 222 for centering. In this state, the magnetic disc 200 is rotated in unison with the disc table 222. The signal recording surface of this magnetic disc 200 is scanned by a magnetic head for recording and/or reproducing information signals.
The magnetic disc 200 is constructed as disc cartridge housed in a main cartridge body unit. The magnetic disc 200 is loaded in this state on the disc drive device and chucked y the disc table 222 for centering with respect to the disc table 222.
The tracking, which is the positioning of the magnetic head with respect to each recording track formed circumferentially on the signal recording surface of the magnetic disc 200, is achieved by radially moving the magnetic head by a stepping motor along the radius of the magnetic disc 200. The amount of feed of the magnetic head along the radius corresponding to each step of the stepping motor is the track pitch.
Meanwhile, it is the rotational torque balance between the magnetic disc 200 and the disc table 222, produced on rotation of the disc table 222, that determines whether or not the magnetic disc has been centered on the disc table 222.
That is, it is determined by the balance between the rotational torque (r) and the torque T(h+s) which is the sum of the torque T(h) produced by contact between the magnetic head and the magnetic disc 200 and the torque T(s) produced by contact with the magnetic disc 200 of a protective sheet, such as a non-woven fabric, used for protecting the signal recording surface of the magnetic disc 200 provided in the main cartridge body unit holding the magnetic disc 200. The rotational torque (r) is the torque with which the disc table 222 and the magnetic disc 200 attempt to rotate in unison by the contacting portions of the disc table 222 and the magnetic disc 200 produced by suction of the magnetic disc 200 by the magnet 224 on the disc table 222 on setting the magnetic disc 200 on the disc table 222 to run the disc table 222 in rotation.
That is, if the level ratio of the rotational torque T(h+s) relative to the torque T(r) is smaller than an optimum value, the magnetic disc is not centered with respect to the disc table 222, but is rotated in the state shown in FIG. 5.
The magnetic disc having the diameter of 3.5 inch, now in wide use, has the recording capacity of 2.5 MB. For processing the program software or data of large capacity, there has been raised a demand for a magnetic disc having a higher recording capacity.
On the other hand, a magnetic disc with a diameter of 3.5 inch, now in extensive use as a recording medium for an information processing device, such as a computer, is desirably used with interchangeability with a disc drive device having a magnetic disc of a larger capacity as a recording medium.
Moreover, the magnetic disc with a diameter of 3.5 inch, so far used, is rotated at a 300 rpm for recording and/or reproducing information signals, and hence has a drawback that it is low in the data transfer rate.